It has long been known that rolling bearings must be lubricated to avoid direct metal to metal contact between rolling bodies, bearing rings, and retainers and the like. The function of the lubricant is not only to prevent wear and avoid metallic contact, but also to prevent corrosion.
It is most advantageous to use a relatively small quantity of lubricant, in which the most advantageous operating temperature for that bearing is achieved. This is accomplished by using precisely the minimum amount of lubricant necessary for reliable lubrication. On those occasions when the lubricant is to provide other functions as well, such as sealing or cooling, the amount of lubricant may be greater.
It is also well known that a lubricant loses its effectiveness over time, due to mechanical work on the lubricant as well as due to aging of the materials from which it is made. A used and polluted lubricant must be replaced and renewed at regular time intervals in order to provide a uniform and effective lubrication of the bearing or other mechanical device. In many instances, rolling bearings are lubricated with grease during the normal service operation of the machine. Grease has a particular advantage, when compared to oil, for example, in that it much more readily stays in the bearing location, particularly in mechanisms including a shaft where the shaft is inclined or is vertical. Grease also provides certain corrosion inhibiting properties which are of value. The choice of the particular grease formulation depends upon the service conditions, which are themselves governed primarily by the temperature range, the speed of operation, and the environment in which the bearing is operating.
In some circumstances, the service conditions require frequent follow on lubrication of the device. Thus bearing housing may, be provided with a particular device such as a bore and nipple to allow grease lubrication. When the bearing is under a heavy load, it can be connected to an automatic lubrication apparatus which continuously provides lubrication to the bearing without the need of supervised or manual work.
These are many automatic lubricating devices on the market today, operating under various different principles. These lubricating devices have serious functional deficiencies which prevents them from providing the intended lubricating effect. Many times, the prior automatic lubricating devices are inferior as an alternative to manual lubrication. Deficiencies occur quite frequently when excessive grease is fed into the bearing, causing a serious increase in bearing temperature, along with the resultant extra wear and other difficulties. Bearing life is reduced at these higher temperatures.
Some automatic lubricating apparatus will fail to lubricate or provide lubrication on an irregular basis. In this circumstance, the devices fail to provide a regular and continuous lubrication which is of extreme importance in demanding applications, such as bearings operating at high speeds and loads. Under these circumstances, rapid changes in operating conditions are magnified and the bearing life is again substantially reduced.
Automatic lubricating devices function basically by feeding the grease to the bearing in a variety of ways. Most common are those which utilize spring biased pistons and those having an electrolytically general driving gas, which acts upon a diaphram connected to a piston.
One method for controlling the amount of oil lubrication to a lubricating device is to adjust the oil supply continuously using heat activatable elements. As an example of such a device, French Patent No. FR-A-877500 shows an oil supply that is normally controlled in such a manner that the oil quantity supplied increases at increasing temperature in the device being lubricated. This is not an adequate solution for a grease lubrication design, however, since an increase in temperature causing an increase of grease lubrication to the bearing would result in an increased temperature of the bearing housing.
Accordingly, it is an object of the present invention to provide a new type of lubricating apparatus for automatic and controlled supply of a lubricating grease to rolling bearings which are mounted in bearing housings.